Polymerization of pyrrolidones and piperidones employing phosphoric anhydride as chain initiators



United States Patent i the recurring unit is one which might hypothetically arise in the condensation polymerization of 4-aminobutyric acid. However, early investigators, namely Gabriel (Berichte 32, 1266 (1899)) and Schotten (Beiichte 21, 2240 (1880)), observed that 4-aminobutyric acid and aminovaleric acid failed to undergo intermolecular condensation and yielded only the five and six membered lactams. The first disclosure of such polyamides was that of USP 2,638,463 (W. O. Ney, W. R. Nurnmy and C. E. Barnes-May 12, 1953), involving the polymerization of pyrrolidone in the presence of an alkaline polymerization catalyst.

While useful polymers are obtained by the process described in the Ney, Nummy and Barnes Patent No. 2,638;

4-63, considerable difliculty is encountered in obtaining these polymers in satisfactory yields; and, also, in the production of polymers having relatively high molecular Weights. Patent No. 2,739,959 of Ney and Crowther, which, in Example I, discloses that only a small yield of low molecular weight polymer may be obtained when an alkaline polymerization catalyst is employed as the sole promoter of the polymerization of pyrrolidone, discloses effecting the alkaline polymerization of the lactams in the presence of a small amount of an acyl compound, as an activator for the alkaline polymerization catalyst; and preferably, carrying out the polymerization of a lactam while dispersed in an anhydrous hydrocarbon nonsolvent therefore, in order to increase the yield and molecular weight of the polymer. The specific activators described in Patent No. 2,739,959, as having the property of increasing the rate of polymerization of lactams having 5- and G-membered rings, are acyl pyrrolidones, acyl dipyrrolidones, organic peroxides, anhydrous lactones and alkyl esters. The Ney and Crowther patent discloses the use of these acyl compounds as activators for the alkaline polymerization catalyst.

I have now found that the oxides of elements of Group V of the periodic table are capable of acting as chain initiators in the alkaline catalyzed polymerization of 5- and G-membered lactams, e.g. pyrrolidone and piperidone. This particular class of oxides of group V elements has the role of initiating chain growth. illustrative of the oxides of group V elements which I have found to be useful as chain initiators in the alkaline catalyst polymerization of pyrrolidone and piperidone are NO, N 0 N204, N02, N205 and P205.

The general conditions and factors utilized for polymerizing 5- and 6-membered lactarns, pursuant to the "ice present invention, may be those mentioned in US. Patent No. 2,739,959, except for the presence of the oxide of a group V and Vi element described in the foregoing, as the chain initiator for the polymerization, in place of the activators specified in that patent. In general, the method of effecting polymerization of 5- and 6-membered ring lactarns, by the process of the present invention is as follows:

initially, there is the preparation of an anhydrous solution of the alkali pyr'rolidone in pyrrolidone. The alkali pyrrolidone usually employed is sodio or potassio pyrrolidone, and may be obtained via the reaction of pyrroh'done with sodium and potassium metal or the respective hydroxides. In the latter case, it is essential to remove the water formed thereby as rapidly as possible. The concentration of the alkali pyrrolidone employed in many instances may vary from 0.5 to 5.0 mole percent, (percentages based on pyrrolidone), and may range from 0.1 to 10.0 mole percent. In series of experiments, optimum yields were obtained with about 2.75 mole percent of alkali pyrrolidone. The role of the alkali pyrrolidone is that of a catalyst and serves as a source of pyrrolidone anions.

The amount of chain initiator employed in many instances may vary from 0.1 to 10.0 mole percent (percentage based on pyrrolidone). The concentration of chain initiator chosen will depend on the conversion desired and the molecular weight sought. The rate of the polymerization will depend, to a large extent, on the molar amount of chain initiator employed, with higher rates obtained by the use of greater amounts of chain initiator. The polymerizations may be chain initiated at temperatures from 25 C. to 65 C. and are accompanied by a mild exothermic reaction.

In a bulk or masspolyrnerization, the addition of the chain initiator is followed by a thickening of the solution and gradual solidification of the mixture. The toughness of the cake will, obviously, depend on the extent of the conversion and will be dependent on the times involved and amounts of chain initiators used.

The polymerization employing the foregoing chain initiators may be conducted in a dispersion of pyrrolidone and the alkali pyrrolidone in a non-solvent for the pyrrolidone. Applicable non-solvents fall in the class of saturated and olefinic aliphatic alicyclic hydrocarbons, i.e., pentane, hexane, heptane, cyclohexane, pentene, cyclohexene, etc. The amount of non-solvent frequently employed is 1 to 3 parts of non-solvent per unit weight of pyrrolidone, but is subject to wide variation. The physical state of the resulting polymer obtained via a dispersion polymerization may vary from a thick curd to a fine powder, depending on conversion desired, ratio of non-solvent to monomer and type as well as rate of agitation.

For the purposes of comparison, there are given below, as examples A and B, illustrations of the prior art polymerization of highly purified pyrrolidone, from the same batch and purified in the same manner as the pyrrolidone used in the examples appearing later in the specification of the process of the present invention:

Example A A 500 cc. glass flask was charged with 100.0 grams (1.18) moles) of highly purified pyrrolidone. There was added 1.0 gram of potassium hydroxide flakes of 83% assay, the system immediately placed under a reduced pressure of 10 mm. and rapidly heated to the reflux point of to C. The vapors were condensed in a vertical reflux condenser maintained at a jacket temperature of 75 0, thus permittin the return of the pyrrolidone and, at the same time, effecting the removal of water. After one hour at the reflux point, the reaction mixture in the still pot was cooled and the clear, colorless solution of potassio pyrrolidone in pyrrolidone allowed to stand for 24 hours at room temperature to the exclusion of atmospheric moisture and carbon dioxide. During the 24 hour period, the mixture became turbid and a scant amount of solid was deposited, The mixture was treated with 400 grams of distilled water, the solid filtered and thoroughly washed with water. The dried polymer weighed 0.6 gram, representing a conversion of 0.6%. The material was of low molecular weight, as indicated by the relative viscosity of a 1% solution in meta cresol.

Example B This example is an illustration of an alternate polymerization of highly purified pyrrolidone, and closely follows Example 1, of U.S. Patent No. 2,739,959, which is also an illustration of prior art polymerization of pyrrolidone. i

A 500 cc. glass flask, equipped for vacuum distillation, was charged with 120.0 grams of highly purified pyrrolidone. There was'added 1.0 gram of potassium hydroxide flakes of 83% assay. The system was immediately placed under a reduced pressure of 1.0 mm. and rapidly heated to eifect the distillation at 90 to 100 C., of 20 grams of pyrrolidone and water. The resulting clear, colorless solution in. the still pot constituted a solution of potassio pyrrolidone in pyrrolidone. The solution was allowed to cool to room temperature and stand for 24 hours to the exclusion of atmospheric moisture and carbon dioxide. During this 24 hour period the mixture became turbid and a scant amount of solid was deposited. The contents were treated with 400 grams of distilled water, the solid filtered and thoroughly washed with water. The dried polymer weighed 0.5 gram, representing a conversion of 0.5% The material was of low molecular weight as indicated by the relative viscosity of a 1% solution in meta cresol.

The details of the present invention will be apparent to those skilled in the art, from the following specific examples, of preferred methods of practicing the same:

Example I This experiment illustrates the use of phosphoric anhydride as the polymerization initiator.

After distilling at mm. about 25% of the monomer from a mixture of 120 g. of pyrrolidone and 3.0 of potassium hydroxide flakes of 83% assay, there remained a residue of 90.7 g. A solution of 0.84 g. of phosphoric anhydride in 10 g. of monomer, prepared by heating the mixture to 150, was added at 32. After a reaction time of 40 hours, the solid polymer was dissolved in 320 ml, of 90% formic acid, reprecipitated with distilled waterv'and washed repeatedly with water until the polymerwater, slurry was essentially neutral, then dried in the vacuum oven to give 38.5 g. of polypyrrolidoneof relative viscosity (c=l, mcresol) 3.997. Based on 95.2 g. of available monomer, the conversion was about 39%.

Example 11 Piperidonemay also be polymerized by a process of the present invention in the same manner as pyrrolidone 'by merely substituting piperidone for pyrrolidone in the foregoing example.

While an N-pyrrolidonylgor N-piperidonyl group ap pears to be the usual chain-terminating group of the polymers obtained, pursuant to the present invention, it'

' lowed by removal of the solvent.

sodium hydroxide, sodium methylate, methanol, ethanol, phenol, ammonio, ethylamine, aniline, diethanolamine. Reaction of the free polymer acid with alkaline agents such as metal hydroxides and amines gives the respective salts. The various terminations proceed through scission of the terminal pyrrolidone ring, or one of the'polyamide linkages, particularly the linkage between terminal pyrrolidonyl linkage and the carbonyl grouping linked thereto. Termination of the polymer chain by means of an ester, such as -NHCH CH CH COOCH may be accomplished by treatment of the polymer intermediate,v

with methanol in the presence of a base.

Hydrolysis of the terminal ring may be accomplished by treating the alkaline containing white' solid, obtained in the polymerization, with water at 7580 C. for one hour. The resulting product is terminated by a products of the present invention, particularly, those of relatively high molecular weight, e.g., products which have a relative viscosity of about 2.5 or higher, as a 1% solution in the m-cresol, are useful for the production of fibers for textile and other usese.g., as insulating blankets, etc. Fibers have been successfully produced from products of the present invention, by drawing from a melt and spinning from solutions, such as solution .in formic acid, followed by evaporation of solvent. Useful films, having a wide variety of applications, may also be produced from the products of the present invention by melt extrusion, and by film-casting from solutions, such as a formic acid solution, glycolic or lactic acid solution, fol- Such films are useful in numerous applications, including electrical applications, as an insulator; as a base for industrial tapes; as a lining material or glass replacement, and in a variety of special packaging applications. I The products of the present invention may also be used in plastic compression molding and extrusion molding applications, where their crystalline nature, sharp melting point and marked fluidity, in themolten state, results in faithful reproduction of the mold. Molded products, for use as containers, may be produced from powders obtained pursuant to the present invention; and, also many mechanical and other engineering parts and materials, such as gears, cams, bearings, and similar machine components may 7 be produced from them. In-the electrical arts, the products of the present invention are useful as a coating on ,wire, etc., as an insulation, and for the production of certain mechanical, electrical parts, such as insulating bushings, fuse holders, andthte like. The products are also of interest in the coating arts as finishes for textiles, paper and similar fibrous materials, and for use as special adhesives and other coatings.

- It should also be understood that theproducts of the present invention may be compounded in many applications with other synthetic plastic materials, plasticizers and fillers. Among the plasticizers, which have been found to be compatible with the products of the present invention, may be mentioned, oand p-toluenesulforn' amide,'-N-ethyl o-- and p-toluenesulfonamide, ethylene carbonate and propylene carbonate.

While the production of polymers of Z-pyrrolidone and Z-piperidone has specifically been described in the foregoing examples it will be apparent that the process of the present invention may be employed for the production of polymers of homologues of 2-pyrrolidone and Z-piperidone which contain a lower alkyl (1-4 carbon atoms) substituent on the carbon atoms in the ring. Such alkyl substituted pyrrolidones and piperidones which have been found to be most readily polymerized by the process of this invention are those in Which certain alkyl substituents in the 3 and 4 position such as 3-rnethyl-2- pyrrolidone, 4-methyl 2 pyrrolidone, 4-ethyl-2-pyrrolidone, 3,3-dimethyl-2-pyrro1idone, 4,4-dimethyl-2-pyrrolidone, '3-methyl-2-piperidone, and 3-ethyl-2-piperidone. The alkyl substituted pyrrolidones and piperidones may be represented by the general formula r RGCR l or EN Z zch 0 0 C N H H 0 wherein Z represents i CH C-C- This application is a division of application Serial No. 726,323 filed April 4, 1

9: 8, now abandoned.

5 I claim: 1. In the process of polymerizing lactams of the formula wherein Z represents Where n is one integer from 1 to 2 and R represents a member of the group consisting of H and lower alkyl groups of 1 to 4 carbon atoms under essentially anhydrous conditions and in the presence of a minor amount up to about 10 mole percent based on said lactam of an alkali metal lactam as the polymerization catalyst; the improvement comprising effecting the polymerization in the presence of a minor amount up to about 10 mole percent based on said lactam of P 0 2. in the process of polymerizing pyrrolidone under essentially anhydrous conditions and in the presence of a minor amount up to about 10 mole percent based on said pyrrolidone of an alkali metal pyrrolidone as the polymer zation catalyst; the improvement comprising effecting the polymerization in the presence of a minor amount up to about 10 mole percent based on said pyrrolidone of P295.

References Qited in the file of this patent UNITED STATES PATENTS 3,057,874 Ney et al. Oct. 9, 1962 

1. IN THE PROCESS OF POLYMERIZING LACTAMS OF THE FORMULA 